The present proposal is an R21 application. The neural substrates that underlie the ability of chronic stress to propel addictive processes and the manner in which drugs alter the physiological sensitivity of stress response pathways are not well understood. We will employ a new approach to the analysis of chronic stress responses using "targeted proteomics," a recently-developed method based upon multi-tissue arrays, computerized image analysis and bioinformatics, to define major trends in the expression of cellular and molecular stress in rats with a vulnerability to cocaine-seeking behavior and rats that have been exposed to specific environmental and pharmacological stressors. Individual differences in noveltyinduced activity have been well described in outbred strains of male rats with High-Responder (HR) rats exhibiting a greater degree of novelty-induced activity relative to Low-Responder (LR) rats. HR rats also exhibit a greater predisposition to drug-taking behavior, and recent data suggest that differences in expression of several stress-related genes in HR vs. LR rats may play an important role in determining individual differences in responsiveness to stress and novelty. Acquisition of cocaine self-administration is also enhanced in rats exposed to a variety of stressors, including isolation conditions, but the question of whether repeated cocaine administration is a chronic stressor itself has not been truly resolved. The protein signature of chronic stress obtained using the targeted proteomics approach will be based on the expression pattern of 41 reporter proteins and provides a broad-spectrum "snap-shot" of key stress response pathways: oxidative stress response, cell detoxification, cell growth regulation, cell adhesion, apoptosis, and neuro-immunoendocrine signaling. In Specific Aim 1, we will test the hypothesis that HR and LR behavioral phenotypes are associated with distinct proteomic signatures of the chronic stress response. Proteomic signatures will be obtained for important nuclei of the overlapping neural reward and stress circuits as well as the skin at several developmental ages. The results will establish whether the proteomic signature of the chronic stress response in the brain and/or skin correlates with the HR and LR behavioral phenotypes, is expressed at birth or develops postnatally, and which tissues are most informative. Skin will be included because it can be sampled repeatedly, unlike brain, and could be used for time-course studies in individual animals. In Specific Aim 2, we will test the hypothesis that isolation housing from weaning to adulthood triggers a chronic stress response which alters the proportion of HR vs. LR rats and produces a distinct proteomic signature, as compared to group-housing In Specific Aim 3, we will test the hypothesis that repeated response-contingent or non-response-contingent cocaine delivery results in distinct proteomic signatures of the chronic stress response as compared to yoked-delivered saline. The proposed study will identify dominant trends in the proteomics of the chronic stress response in reward and stress circuits of the brain that are associated with the HR and LR behavioral phenotypes as well as with chronic exposure to specific environmental or pharmacological conditions. Validating the use of skin for assessment of the chronic stress status of rats will provide the basis for simple and practical monitoring of the impact of chronic stress in both animal and human studies. Trends in the chronic stress response discovered in this exploratory study will greatly facilitate detailed investigations of proteins and molecular pathways that may confer an increased vulnerability or decreased resistance to drug use.